Compact fast imaging spectrometer

Abstract

A spectrometer construction incorporates a single lens system (11) to both focus light input to the spectrometer on a diffraction grating (9) and to focus the light dispersed by the diffraction grating into separate spectral constituents back through that lens onto an image plane (15) for processing. Ordinary photographic lenses with fast lenses of f2 or better are able to serve as the lens system, thereby providing a higher quality system at lower cost than previously possible. With the light path doubling back through the spectrometer lens the space required for a spectrometer's optical system is reduced and results in a more compact spectrometer.

What is claimed is: 
     
       1. A spectrometer for analyzing spectral content of incident light comprising: a spectrometer lens; said spectrometer lens having an objective end, an image plane end and a central axis and containing multiple lenses, with individual ones of said lenses being located at selected positions along said central axis;   light slitter means for receiving light incident on one side thereof and passing a narrow slice of that incident light to the other side thereof;   a telescopic imaging lens for focusing an image of light at said light slitter means;   mirror means;   said mirror means being disposed to one side of said light slitter means for receiving said narrow slice of incident light from said light slitter means and reflecting said narrow slice into said image plane end of said spectrometer lens, whereby said spectrometer lens collimates said narrow slice and issues said narrow slice from said objective end;   a diffraction grating disposed at said objective end of said spectrometer lens for receiving collimated light from said objective end and reflecting spectrally dispersed spectral lines of that light into said objective end;   an image plane, said image plane being disposed behind said image plane end of said spectrometer lens system and to one side of said mirror means for receiving spatially arranged straight spectral lines issuing from said image plane end of said spectrometer lens; and   image pick up means for imaging a two dimensional area at said image plane, said image pick up means being positioned at said image plane to individually detect the illumination intensity of multiple portions of the length of each straight spectral line present at said image plane.   
     
     
       2. The invention as defined in claim 1, wherein said image pick up means comprises: electronic camera means, said electronic camera means including a two dimensional photosensitive surface for receiving two dimensional images of light and outputting information of said received two-dimensional image in electronic form; and wherein said photosensitive surface is positioned at said image plane.   
     
     
       3. The invention as defined in claim 1, further comprising: display means, coupled to said image pick up means, for displaying a visually perceptible two-dimensional display of an image picked up by said image pick up means.   
     
     
       4. The invention as defined in claim 3, wherein said said electronic camera means further comprises a charge-coupled device two-dimensional array, whereby the intensity of each portion of the length of each spectral line presented at said image plane is individually monitored. 
     
     
       5. The invention as defined in claim 2, wherein said electronic camera means comprises: a two dimensional array of infra-red light detectors, whereby the infra-red intensity of each portion of the length of each spectral line presented at said image plane is individually monitored. 
     
     
       6. The invention as defined in claim 2, wherein said image pick up means further comprises photographic film. 
     
     
       7. The invention as defined in claim 1, wherein said spectrometer lens comprises a multi-element f3.5, 135 millimeter telephoto lens. 
     
     
       8. The invention as defined in claim 4, wherein said spectrometer lens comprises a multi-element f3.5, 135 millimeter telephoto lens. 
     
     
       9. The invention as defined in claim 1, wherein said spectrometer lens comprises a multi-element f3.5, 135 millimeter telephoto lens and wherein said telescopic imaging lens comprises a 17.5 inch Newtonian lens. 
     
     
       10. A spectrometer for analyzing spectral content of incident light comprising: a spectrometer lens; said spectrometer lens having an objective end, an image plane end, a central axis and multiple lenses;   light slitter means for receiving light incident on one side thereof and passing a narrow slice of that incident light to the other side thereof;   a telescopic imaging lens for focusing an image of light at said light slitter means;   mirror means;   said mirror means being disposed to one side of said light slitter means for receiving said narrow slice of incident light from said light slitter means and reflecting said narrow slice into said image plane end of said spectrometer lens, whereby said spectrometer lens collimates said narrow slice and issues said narrow slice from said objective end;   light dispersing means disposed at said objective end of said spectrometer lens for receiving collimated light from said objective end and reflecting spectrally dispersed spectral lines of that light into said objective end;   an image plane said image plane being disposed behind said image plane end of said spectrometer lens system and to one side of said mirror means for receiving a spacially arranged spectral lines issuing from said image plane end of said spectrometer lens; and   image processing means for collecting a two dimensional image of said image plane containing each incident spectral line and processing said image.   
     
     
       11. The invention as defined in claim 10, wherein said image processing means further comprises: electronic camera means. 
     
     
       12. The invention as defined in claim 11, wherein said electronic camera means further comprises a two-dimensional array charge coupled device.